Finishing polyester fabrics



United States FINISHING PGLYES'I'ER FABRICS Navin J. Gajjar, Wilmington,Deb, assignor to E. 1. du Pont de Nemours and Company, Wilmington, Del.,a corporation of Delaware No Drawing. Application December 12, 1956Serial No. 627,743

Claims. (CI. 28-76) also known to heat-treat polyester fabrics prior tocaustic treatment for the purpose of further improving fabricproperties. Both of these known treatments improve drape and livelinessof polyester fabrics.

It is an object of this invention to provide polyester fabrics havingimproved aesthetics. to provide a new method of finishing said fabricsto improve their handle. Another object is to provide a method forproducing a pattern-less fabric composed of polyethylene terephthalateyarns and having a handle resembling that of silk fabrics. Other objectswill appear in the description which follows.

'In accordance with this invention a fabric comprising polyester yarnsis calendered at elevated temperature and pressure and then treated withan aqueous solution of an inorganic alkaline material until there is afabric weight loss of at least 5%. In a preferred embodiment a fabricwoven from polyethylene terephthalate yarns is calendered at atemperature of 100 F.-450 F. under a pressure of from about 0.12 tonsper linear inch to about 2 tons per linear inch, followed by subjectingthe fabric to dry heat while it is partially relaxed at a temperature offrom about 250 F. to about 450 F. until the fabric has shrunk at least3% warpwise and at least 3% fillingwise and then subjecting the fabricto hydrolysis in the presence of an aqueous solution of an alkalinematerial such as an alkali metal hydroxide or alkali metal salt derivedfrom a weak acid or an alkaline earth metal hydroxide to produce afabric weight loss of 5%25%.

The purpose of the calendering step is to flatten the fabric surface andas a result of this treatment the cross section of the fibers of thefabric is deformed. The calendered fabric also has a noticeablechintz-like glaze on the surface. In order to accomplish the desiredchanges in the fabric by means of the calendering opera tion severalvariables must be controlled. First, the temperature should be in therange of 100 F.450 F. and preferably 100 F.-350 F. Pressure on thefabric surface should be maintained in the range of 0.12 ton per linearinch to 2 tons per linear inch, and preferably between about 0.2 andabout 0.8 ton per linear inch. Rate of the calendering depends on thetemperature and pressure employed and the results desired in theparticular fabric being treated. Typically the fabric is calendered atbetween about and about 100 yards per minute. Fabric construction Willalso affect the properties of the finished fabric. It will be obvious tothose skilled in the art that the proper fabric construction must bechosen in order to obtain the particular body and handle desiredin thefinished fabric. 7

One of the most important factors in the calendering operation is thenature of the surface of the calender A further object is roll. In orderto achieve the most desirable results of this invention the fabricsurface must be deformed uniformly throughout its area by contacting atleast 50% of the surface area of the fabric with calender rolls. Thismay be accomplished using either a standard smooth surfaced, highlypolished stainless steel calender roll, which compresses and deforms ofthe fabric surface area, or a Schreiner roll which is a steel rollhaving many fine lines per inch engraved hit, and which, depending uponthe number of lines, will compress about 50% or more of the fabricsurface during calendering. Failure to deform at least 50% of the fabricarea during calendering produces fabrics which are deficient in surfacecover and dryness. A Schreiner or smooth calender roll is normallycomplemented by a standard hard smooth paper covered husk rollcontacting the other side of the fabric in order to obtain the necessaryamount of pressure against the fabric surface.

In addition to compressing at least 50% of the fabric area thecalendering step in this invention should not leave any pattern, visibleto the unaided eye, on either fabric surface. The deformation'of thefabric is obtained on only one surface at a time in contrast toembossing rolls which contact and compress both sides of the fabric andleave a defined visible pattern on both surfaces. Moreover, because thefinest patterned embossing rolls will not deform anywhere near 50% ofthe fabric area, embossed fabrics lack the surface dryness and coverobtainable by this invention.

When in the calendering treatment temperatures approaching 450 F. areemployed, the finished fabric retains too much plastic-like handleunless excessive caustic treatment follows the heat treating step. Inorder to keep the caustic treatment at a minimum, and thereby reducefabric weight'loss and cost, the fabric'may be scoured relaxed at theboil after calendering. After this additional scouring, the fabric isdried, heat-set, and treated with caustic. This alternative procedureremoves any excessive plastic-like handle with only about 10% fabricweight loss instead of as much as 20%-35% weight loss in the case ofcertain types of fabrics which have not been scoured followingcalendering.

After calendering, the fabric is subjected to dry heat at a temperatureof 250 F. 450 F. for a period of time sufficient to heat-set the fabricin order to obtain optimum drape and liveliness. In this heat treatingstep the fabric may be either relaxed or unrelaxed. The fabric isheatset if the fabric is treated in at least a partially relaxedcondition at the above temperature for a time sufficlent to permitshrinkage of at least 3% Warpwise and 3% fillingwise or treated the samenumber of minutes at the same temperature in an unrelaxed condition.Thus the time required for heat-setting the fabric under unrelaxed (notfree to shrink) conditions is the time in minutes required to heat-setthe same fabric at the same temperature under relaxed (free to shrinkcondition). Preferably the fabric is partially relaxed during heattreatment so as to allow the fabric to shrink somewhat in the warp andfilling. Heat treatment under at least partially relaxed conditionsresults in higher liveliness, surfajce'dryness and drape and lessthreadiness in the finished fabrics than is obtained in fabrics that areheat-set unrelaxed according to the process of this invention. In someare generally not as good as with a separate heat t'reatf ment step. p

After heat-setting, the fabric is hydrolyzed to'remove part or all of.the glaze orplastic like handle produced on the surface of the fabric bycalendering, as well as to generally improve the fabric handle. Thisstep in the process further modifies the cross-section of the componentfibers by preferentially dissolving part of the. fiber surface, therebyaccentuating the deformed cross-section. produced by the cal'enderingstep, which introduces random high and low points in the surface of. thefiber cross-section.

Hydrolysis may be carried out by treating the fabric with an aqueousmedium containing inorganic alkaline material capable of producing aweight loss in this step of at least Preferably this weight loss is heldto a minimum, e. g., 5%25%, depending upon the type and construction, offabric employed, in order to keep the process economical. However, incertain instances where it is desired to produce extremely high drapeand liveliness in the final fabric, the weight loss may be extended toas much as 50%. Suitable alkaline materials include sodium hydroxide,which is preferred because of its availability and low cost, potassiumhydroxide, and salts thereof derived from weak acids, said salts beingcharacterized by a pH of at least 12 in 0.1 N aqueous solution. Examplesof useful salts include alkali metal sulfides, alkali metal sulfites,alkali metal phosphates and alkali metal silicates. Other suitableinorganic alkaline materials include calcium hydroxide, bariumhydroxide, strontium hydroxide and the like.

Concentration of the alkaline material in the aqueous hydrolysis bath ispreferably at least 2% based upon the bath weight. Concentration ofalkaline material, the fabric exposure time in the bath, and thetemperature of the hydrolysis bath may be varied at will to produce thedesired weight loss in the fabric. Normally it is convenient to immersethe fabric in an aqueous solution of the desired alkaline material andto have the bath at or near normal boiling temperature at atmosphericpressure. In some cases it may be desirable to employ lower temperaturesand longer times. Hydrolysis reduces the size of the yarn to a finerdenier than that in the original fabric.

After hydrolysis the fabric is generally rinsed with water, scoured witha dilute aqueous acid wash, and rinsed again, to remove any residualalkaline material remaining. The fabric then is dried at ordinarytemperatures, usually at 200 F.240 F.

Although the process of this invention has. been de scribed with respectto treating fabrics composed of polyethylene terephthalate yarns, itshould be understood that the invention is likewise applicable toimproving the handle of fabrics made from other polyester andcopolyester yarns. Preferably the yarns will be composed of polyestersin which at least 90% of the recurring structural units are ethyleneterephthalate units, with any residues present comprising otherdicarboxylic acids or other glycols. For example, the ethyleneterephthalate copolyester may contain residues of sebacic acid,isophthalic acid, sodium sulfoisophthalic acid, or butylene glycol.Furthermore, the fabrics finished by this invention may be composed ofyarns prepared from fibers and filaments having odd cross-sections, forexample, in the shape of ribbon, dogbone, cruciform, Y-shaped, and thelike, as well as the conventional circular cross-section.

Woven fabrics of this invention are composed of at least 50% by weightof polyester fibers or filaments. That is, the fabrics may be made fromblends of polyester fibers with other synthetic and natural fibers,providing the fabric is free from wool and other components which wouldbe deleteriously affected by the caustic treating step in the process.Other fibers that may be blended, plied, and twisted or otherwise mixedduring weaving with polyester fibersinclude those made from polyamidesand polyurethanes and their copolymers, acrylic polymers and copolymers,cellulose derivatives such as cellulose acetate, regenerated cellulose,cotton and the like.

Fabrics finished by the process of this invention exhibit a verydesirable handle along with other improved properties. These fabricsexhibit improved drape and suppleness (which may be measured, forexample, by flexural rigidity), improved surface dryness, increasedsurface friction, liveliness, and luster, improved resilience, increasedsurface cover and opaqueness, and reduced threadiness. In addition, thetreatment reduces yarn shiftiness in the fabric. In many respects thefinished fabrics appear like silk and have similar scroop and rustle.The process of this invention yields fabrics that have good handle andsilk-like appearance in addition to good surface covering power anddryness which is unattainable in fabrics that have been heat-set andcaustic treated without the combination with the preliminary calenderingtreatment.

Examples of typical fabrics which may be processed by this inventionincludes taifetas, georgettes, sand-crepes, tissue-failles, foulards,broadcloths, batistes, light weight suitings, dress and blouse fabrics,shirtings, lingerie, and rainwear.

The following examples iliustrate specific embodiments of thisinvention. All parts and percentages are by weight unless otherwiseindicated.

In the examples flexural rigidity (which is a measure of the supplenessand drape of a fabric, the lower the value the better the drape) ismeasured by the hanging heart method originated by Pierce (Journal ofthe Tex tile Institute, 21, T377, 1930) and performed as. described byHoifman and Beste in Textile Research Journal, XXI, No. 2, 66 (February,1951).

Contact covering power in percent (I Which is a measure of the surfacecover, is determined by measuring the effect of background color on thereflectance of the fabric when exposed to a light source. Therefiectance values in the equation below are determined using aPhotovolt Reflectometer, Model 610 (Photovolt Corporation):

W B)( rW-Rrn) Rw-RB where R =Reflectance of fabric on black backgroundin per:

cent. R =Refiectance of fabric on white background in percent. 7

The coefficient of surface friction (which is-a measure of the surfacedryness of the fabric, value the drier the fabric) is determined mula:

where e is the total contact angle in radians (the sum of the threeangles formed by the suspended fabric as a result of its contact withthe three probes), and T5 is the weight in grams attached to the bottomof the suspended fabric. The surface friction is measured by using amodified Instron tensile tester. Thes tester is modified so that amovable probe is positioned in the same plane and in horizontalparallel'opposed relationship with two separated fixed probes, so thatthe movable probe can be advanced between the two fixed probes. Allthree probes are covered with samples of the test fabric. Preparatory totesting, a stationary weighted sample of the same test fabric issuspended vertically with the movable probe on one side and the fixedprobes on the other. The movable probe is first advanced, pushing thesuspended fabric between the two fixed probes and forming an angle inthe suspended fabric at each line of contact with a probe. As the crosshead of the Instron tester is lowered, the three fabric covered probesurfaces,which are fixed spatially with respect to each other and whichare in frictional contact with the suspended. fabric, are drawn alongthe length of the suspended stationary fabthe higherthe from the f01-..

ricx The dynamic and staticforcesrequired to over come the frictionbetween the suspended fabric and the covered probes are recorded on theInstron tester. These forces in grams are averaged and the average forcereported as T in the formula above. 1

EXAMPLE I A continuous filament polyethylene terephthalate yarn, having34 filaments and a total denier of 70, is woven into a plain weavefabric of 136 x 95 construction,

weighing 2.5ounces per square yard. This fabric is taken from the loomand scoured at 180 F. with 2% soap solution for two passes at a fabricspeed of 2 yards per minutes. After scouring, thte fabric is dried atwet dimensions on a pin-tenter frame at 225 F. The fabric is calenderedbetween a smooth stainless steel roll and a-smooth husk roll at 350 F.,0.5 ton/linear inch pressure and 25 yards per minute fabric speed. Thefabric is heat-set on a pin-tenterat 440 F. for one minute exposure with5% overfeed in warp direction and two inches under width. After heatsetting, the fabric is immersed for five minutes in a boiling causticsolution containing 3% by weight of sodium hydroxide, the weight of thesolution being about 50 times the weight of the fabric. ,The' caustictreated fabric is removed and rinsed with. warm water for five minutes,treated with 1% acetic acid for ten minutes, rinsed again with warmwater for 5 minutes, and finally dried at about 225 F. The resultantfabric lost approximately 25% of its weight during the caustictreatment. The fabric now has a drier, livelier and a much moredesirable silk-like handle than the original control fabric. Table Ishows some physical characteristics of the fabric.

Table I A 2 x 2 twill foulard fabric of 264 x 102 construction, weighingapproximately 1.8 ounces per square yard, is woven from polyethyleneterephthalate filament yarn. The warp is made of 30 denier yarn, having30 filament, 7 Z turns per inch, and the filling of 60 denier yarn,having 60 filament, 3.5 Z turns per inch. The fabric is taken from theloom, and scoured, dried and calendered, as in Example I. In thisexample, the fabric is not heat-set after calendering, as in the firstexample, but is treated in a caustic bath and rinsed as described inExample I.

The treated fabric exhibits a much more desirable handle than theoriginal control fabric as shown in Table II, and is silk-like.

In this example, fabric and finishing treatment are the same as inExample I, except that during heat-setting, the fabric is completelyrelaxed (i. e., it is allowed to shrink to the maximum extent possiblein the pin-tenter).

Warpwise shrinkage is 6% and fillingwise shrinkage is The treated fabricexhibits a much more desirable and silk-like handlethan the originalcontrol fabric, as'sh'own In this example, fabric and finishingtreatment are the same as in Example 1, except that a stainless-steelSchreiner roll is used instead of a smooth surfaced calender roll. TheSchreiner roll contacts about 60% ofthe fabric surface duringcalendering. The treated fabric is silklike and exhibits a muchdriersurface handle than even the finished fabric obtained in Example I.

Table IV Weight 7 Flexural Surface Fabric (Oz./Sq.Yd.) 'RigidityFriction (mg. cm.)

Untreated Control (scoured)- 2.5 38.8 0.249 Example IV 1. 9 16. 1 0; 328

EXAMPLE V Polyethylene terephthalate yarn having 34 filaments and atotal denier of 70 is woven into a plain weave of 112 x 86 construction,weighing 1.83 ounces per square yard. This fabric after weaving is crabscoured at 212 F. with 2% soap solution and dried at 225 F. 'The dryfabric is calendered on a stainless steel Schreiner roll at 300 F. and0.6 ton/linear inch pressure once on each side of the fabric. The fabricis backed up by a smooth hard paper covered husk roll. The Schreinerroll has 260 diagonal lines per inch at a 60 angle and contacts about60% of the surface area of the fabric. Each lines cross-sectionrepresents an equilateral triangle having a dimension of 0.0037 inch oneach side, while the crosssection of the Schreiner roll surfaceresembles that of a saw tooth. After calendering, the fabric is crascoured again at 212 F. and dried at 225 F. It is heat-set at drydimensions (i. e., unrelaxed) at 440 F. for one minute, and thenimmersed in an aqueous solution containing 3% by weight sodium hydroxideat 212 F. for 90 minutes. The fabric is removed from the causticsolution, rinsed in water to remove excess alkali and dried at 215 F.The resulting fabric showed a weight loss of 19.7% in the caustictreating step. The finished fabric has good drape, suppleness,liveliness and cover, in

addition to the properties shown in Table V.

The control fabric in Table V was given a standard commercial finishingtreatment involving scouring at 212 F. with 2% soap solution, drying at225 F., and then heat setting by subjecting the fabric to dry heat at360 F. for 45 seconds. It was not calendered or treated with caustic.

EXAMPLE VI A spun yarn of 60 cotton count made from 65% polyethyleneterephthalate fibers (1.2 denier per filament and 1.5 inches in length)and 35% cotton fibers is woven into a plain weave of 120 x 68construction. This fab-' ric, after weaving, is crab scoured at 212 F.with 2% soap solution and dried at 215 F. The dry fabric is calenderedon a stainless steel Schreiner roll at 275 F. once on each side of thefabric using 0.6 ton/linear inch pressure, using the same Schreiner rollas in Example V. The fabric is backed up by a smooth hard paper-coveredhusk roll. After calendering, the fabric is crab scoured again at 212F., then dried at 215 F. The fabric is heat-set at dry dimensions (i; e.unrelaxed condition) at 440 F. for one minute, then treated with anaqueous solution containing 3% by weight sodium hydroxide at 212 F. for60 minutes. The fabric is removed from the caustic solution and rinsedin water to remove excess alkali and then dried at 215 F. The resultingfabric showed a weight loss of 6.8% in the caustic treating step. Thefinished fabric has good drape, suppleness, liveliness, and cover. Inaddition, the fabric has improved uniformity (reduction in visible reedmarks, reduction in unevenness of yarn bundle, and an over-all betterappearance) in comparison with a fabric of equivalent construction whichhas been finished by a scour and heat-set treatment, but has had nocalendering or caustic treatment.

I claim:

1. A process for treating a polyethylene terephthalate tween about 100F. and 450 fabric which comprises deforming the fabric by means ofcompressive force applied to at least of the sur face area of the fabricand distributed uniformly over the entire surface area of the fabric ata temperature be- F., heat setting the fabric by subjecting it to dryheat at a temperature from about 250 F. to about 450 F. and thenimmersing the fabric in an aqueous alkaline solution until the fabrichas lost at least 5% in weight, followed by washing and drying thefabric.

2. The process of claim 1 in which the fabric is compressed bycalendering at a temperature between about F. and 350 F. at a pressureof between about 0.12 ton and about 2 tons per linear inch.

'3. The process of claim 2 in which the aqueous solution contains analkali metal hydroxide.

4. The process of claim 3 in which the fabric is 100% polyethyleneterephthalate.

5. The process of claim 4 in which the alkali metal hydroxide is sodiumhydroxide.

2,712,170 Phillips July 5, 1955 Knapp Feb. 12, 1957.

1. A PROCESS FOR TREATING A POLYETHYLENE TEREPHTHALATE FABRIC WHICHCOMPRISES DEFORMING THE FABRIC BY MEANS OF COMPRESSIVE FORCE APPLIED TOAT LEAST 50% OF THE SURFACE AREA OF THE FABRIC AND DISTRIBUTED UNIFORMLYOVER THE ENTIRE SURFACE ARE OF THE FABRIC AT A TEMPERATURE BETWEEN ABOUT100*F. AND 450*F., HEAT SETTING THE FABRIC BY SUBJECTING IT TO DRY HEATAT A TEMPERATURE FROM ABOUT 250*F. TO ABOUT 450*F. AND THEN IMMERSINGTHE FABRIC IN AN AQUEOUS ALKALINE SOLUTION UNTIL THE FABRIC HAS LOST ATLEST 5% IN WEIGHT, FOLLOWED BY WASHING AND DRYING THE FABRIC.